1. Field of the Invention
The present invention relates to a phenolic resin, designed to be used in a sizing composition for mineral fibers. This resin is produced from the condensation of phenol, formaldehyde, amine, and urea.
The present invention also relates to a procedure for the preparation of a phenolic resin and for a sizing composition that contains said resin for bonding mineral fibers.
The present invention further relates to the use of sized mineral fibers for the manufacture of insulating products and for products designed to form soilless cultivation substrates.
2. Discussion of the Background
Mineral fiber-based products may be produced from fibers obtained using various procedures. Mention may be made of the conventional centrifugal stretching technique, in which molten material, which is placed in a centrifuge containing a multitude of small holes, is thrown against the peripheral centrifuge wall by centrifugal force, and escapes through the holes in filament form. Upon exiting from the centrifuge, these filaments are stretched and driven to a collection apparatus by a high-speed, high-temperature gas current, so as to form a layer of fibers. To bond the fibers together, a composition, called a sizing composition, containing a thermosetting resin, is sprayed on the fibers as they travel to the receiving device. The layer of fibers treated in this manner is then subjected to a thermal treatment in an oven, in order to polycondense the resin and obtain an insulating product exhibiting the desired properties, such as dimensional stability, resistance to traction, retention of thickness after compression, and homogeneous color.
The sizing compositions, to be sprayed on the mineral fibers, contain a resin which is generally an aqueous compound further containing urea and additives such as silane, mineral oils, liquid ammonia, ammonium sulfate, and water.
In accordance with the invention, resin is defined as a product of condensation of reactive starting materials in the presence of a catalyst, prior to any baking phase in an oven.
The properties sought for the sizing compositions are dependent to a large extent on the properties of the resin. A sizing composition must, above all, possess a high spraying capacity, coating and fiber-bonding properties, and must, at the same time, not pollute to any significant degree.
To possess these properties, the resin must, in particular, exhibit good stability over time and be highly dilutable in water.
The resin must be stable, especially for at least eight days at 12.degree.-18.degree. C. Indeed, it must be possible to preserve it for several days before using it to make the sizing composition. The sizing composition containing the aforementioned resin and additives, is normally prepared at the time of use.
The resin must, moreover, possess a high degree of dilutability in water. Dilutability is a particularly important factor, since the sizing composition containing the resin is then suitable for spraying. Dilutability is generally defined as follows: dilutability in water of a resin in the form of an aqueous compound is the volume of deionized water which, at a given temperature, can be added to the unit of volume of that compound before causing formation of permanent turbidity.
The dilutability in water of a resin capable of being used in a sprayable sizing composition must preferably be equal to or greater than 1,000% for at least eight days at 20.degree. C.
Furthermore, the resin must be as free as possible from unreacted starting materials. The risks of atmospheric pollution results basically from the presence of volatile monomers: these include the starting materials needed to produce the resin, i.e., formaldehyde and phenol which remain unreacted during the reaction or are reformed during sizing of the fibers or at a later stage.
Accordingly, to obtain sizing compositions in which the pollution-generating-agent content, and most notably the free phenol and free formaldehyde content, is as low as possible, the resin must contain the smallest possible quantity of unreacted starting materials, while at the same time preserving its properties.
These two objectives, i.e., a stable resin containing small quantities of free formaldehyde and phenol which, at the same time, preserves the desired properties, in particular a high degree of dilutability in water facilitating spraying on the mineral fibers, are mutually contradictory. Reduction of the free phenol and formaldehyde contents is generally obtained by increasing the condensation rate (i.e., % conversion of phenol and formaldehyde), however this has the consequence of, reducing dilutability.
Conventional practice calls for the preparation of resins that can be used for mineral-fiber sizing compositions by reacting phenol and formaldehyde in the presence of an alkaline catalyst. To promote the phenol-formaldehyde reaction and to thus reduce the quantity of non-reacted phenol and avoid pollution risks, conventional practice prescribes the use of a formaldehyde/phenol mol ratio greater than 1, and, to react the excess formaldehyde, by the addition of urea. Resins formed from condensates of formaldehyde-phenol and urea-formaldehyde are thus formed.
Accordingly, as described in U.S. Pat. Nos. 4,663,419 and 4,710,406, it has proved possible to obtain a resin in liquid form resulting from the condensation, in an alkaline medium, of formaldehyde, phenol, and urea, possessing a dilutability in water of at least 1,000%, and containing a free phenol and a free formaldehyde content of less than or equal to 0.5% and 3%, respectively, of the total weight of the liquid. This resin thus obtained has a formaldehyde/phenol mol ratio of between 3 and 6. The proportion of phenol and formaldehyde is measured as a percentage of the total fluid weight.
This resin is considered to have satisfactory properties permitting its use in sizing compositions for mineral fibers and to be relatively non-polluting.
While the free phenol content can be considered fairly low and to cause little pollution, the free formaldehyde content in the resin (3%) is still high. Attempts have thus been made to reduce it still further, while preserving the resin properties for the ultimate use desired.
Furthermore, the use of a high formaldehyde/phenol mol ratio, as described in the above-mentioned U.S. Pat. Nos. 4,663,419 and 4,710,406, makes it possible to substantially reduce the free phenol content; however, it requires the use of urea to react with the excess formaldehyde. The result is the formation of a urea-formaldehyde condensation product which is not particularly stable when heated.
The thermal instability of urea-formaldehyde and condensation products constitutes a problem, since the mineral fibers treated by the sizing composition are subjected to a thermal treatment so as to obtain a product used for insulation.
In fact, when the resin is used for sizing mineral fibers, the resin is exposed to temperatures of more than 100.degree. C., and the urea-formaldehyde condensation product releases formaldehyde under the effect of heat, thereby increasing atmospheric pollution. A need therefore continues to exist for a sizing composition with reduced emissions.